1. Field of the Invention
The present invention relates to an offset measurement method, a tool position detection method and a bonding apparatus. More specifically, the present invention relates to a method and apparatus that allows the accurate calculation of the amount of offset between a position detection imaging device and a processing member such as a tool.
2. Prior Art
In bonding apparatuses, such as a wire bonding apparatus, a bonding head is mounted on an XY table. On this bonding head, a position detection camera and a bonding arm are provided. The position detection camera is used to image a reference pattern on objects to be bonded such as semiconductor devices, etc. in order to specify the bonding points on these objects to be bonded. The bonding arm has a tool on its one end so that the tool performs bonding on the objects to be bonded. The position detection camera and the tool are installed so that the optical axis of the position detection camera and the axial center of the tool are shifted by a fixed distance. This arrangement is made so that the tool and bonding arm do not interfere with the visual field of the position detection camera when the position detection camera images the reference pattern on the object to be bonded. Generally, the distance or the between the optical axis of the position detection camera and the axial center of the tool is referred to as the xe2x80x9coffsetxe2x80x9d.
Since the position detection camera determines the reference point that is used in order to ascertain the position to which the tool is moved, it is extremely important to ascertain exactly how far the position detection camera is offset from the tool. However, since the actual amount of offset varies from instant to instant as a result of thermal expansion of the camera holder and bonding arm caused by radiant heat from the high-temperature bonding stage, the amount of offset must be corrected at the time that bonding work is initiated and with an appropriate timing during the bonding work.
For this purpose, Japanese Patent Application Laid-Open (Kokai) No. S59-69939, for instance, discloses a method that corrects the amount of offset. In this method, a pressure mark is formed by a tool at a suitable location within a bonding range, the position of the tool is detected by a position detection camera to detect the position of pressure mark, and the amount of offset is corrected based upon this position. In this method, the center coordinates of the pressure mark are determined by performing specified image processing on image data obtained by photoelectric conversion from the position detection camera, and the amount of offset is calculated based upon these coordinates.
However, in the above-described conventional construction, the pressure marks of the tool are not always distinct. Furthermore, unlike cases in which a special pattern suitable for image processing is used, the shapes of the individual pressure marks differ from each other. Thus, detection is not always accurate.
The present invention solves the above-described problems.
The object of the present invention is to provide a novel means that accurately detects the position of a bonding tool.
The above object is accomplished by the unique structure for a bonding apparatus and an offset method that is used in such a bonding apparatus that is comprised of:
a position detection imaging device which images an object to be processed, and
a tool which is installed at an off set position with respect to the position detection imaging device,
and in the present invention:
a reference pattern is projected toward the tool at a specified angle of inclination with respect to a measurement direction from a light source that is disposed in a specified position,
the position of the tool is measured based upon the reference pattern projected on the tool,
the position of the position detection imaging device is measured, and
the amount of offset between the position detection imaging device and the tool is determined based upon these measurement results.
In the present invention, the reference pattern is projected on the tool (bonding tool) at a specified angle of inclination with respect to the measurement direction from the light source disposed in a specified position, and the position of the tool is measured based upon the reference pattern that is projected on the tool. Thus, since the reference pattern projected on the tool is detected with a position and shape that differs according to the position of the tool, the position of the tool is accurately detected based upon such detected different positions and shapes.
Furthermore, the position of the position detection imaging device (a position detection camera) is measured by imaging the specified reference point by the position detection imaging device. Accordingly, the position detection imaging device that is used to image the object to be processed can be used to measure offset amounts.
In the present invention, a reference member disposed in a specified position is used as the reference point. Also, the projection of the reference pattern onto the tool and the measurement of the position of the tool are both accomplished in an attitude in which the tool is caused to approach the reference member. In addition, when the amount of offset between the position detection imaging device and the tool is determined, the amounts of movement of the position detection imaging device and tool between an attitude in which the position of the tool is measured and an attitude in which the reference point is imaged by the position detection imaging device can be specified. As a result, the position of the tool and the measurement of the position of the position detection imaging device is measured with great accuracy because of the use of the reference member.
Furthermore, in the present invention, it is possible so set so that the reference pattern is projected on both the tool and the reference member from the light source and that the position of the tool is measured based upon the image light from the tool and the reference member. As a result, the positional relationship between the reference member and the tool can be determined with good precision based upon the positional relationship between the tool and the light source and upon the positional relationship between the reference member and the light source.
In the present invention, when the position of the tool is measured, it is possible to design so that an image light from the tool and the reference member is conducted to the position detection imaging device. With this structure, the position detection imaging device that is used to image the object to be processed can be used not only for detecting the position of the position detection imaging device but also for detecting the position of the tool.
In addition, the measurement of the position of the tool can use two measured values. One is that which is obtained by measuring the position of the tool based upon the reference pattern projected on the tool. The other is that which is obtained by conducting image light from the tool and the reference member to the position detection imaging device and then measuring the positional relationship between the tool and the reference member by the position detection imaging device. In this way, the tool position can be measured more accurately.
The present invention further provides a method for detecting the position of a tool that processes an object to be processed. This method of the present invention comprises:
a step in which a reference pattern is projected on the tool and a reference member disposed in a specified position from a light source disposed in a specified position, and
a step in which the position of the tool is measured based upon the reference pattern projected on the tool and the reference member.
In this method, the reference pattern is projected on both the tool and the reference member, and the position of the tool is measured based upon the reference pattern projected on the tool and the reference member. Accordingly, the positional relationship between the reference member and the tool is determined with good precision based upon both the positional relationship between the tool and the light source and the positional relationship between the reference member and the light source.